Minimizing secondary cooling air leakage through the wheel spaces may increase overall turbine performance and efficiency. The sealing mechanism should effectively seal between rotating components such as buckets, blades, disks, and spacers and stationary components such as nozzles, vanes, and diaphragms. Specifically, the hot gases flowing through the turbine should be prevented from “ingesting” or leaking into the wheel spaces between the rotating components attached to the rotor and the stationary components attached to the turbine shell.
The wheel space cavities may be pressurized to provide a positive outflow from the wheel spaces into the gas path. Angel wing type seals also may be used to minimize this outflow by restricting the gap through which the leakage may occur. These seals also create a pressure loss “labyrinth/seal tooth” mechanism to further reduce the outflow of the wheel space air.
A drawback with the angel wing type designs is that the gas path pressure profile may vary circumferentially, particularly downstream of the buckets. In order to prevent ingesting, the wheel space pressure should exceed that found at peak pressure locations. Current angel wing configurations, however, generally only provide a near uniform annular pressure throughout. At low gas path pressure locations, such as downstream of the suction side or concave side of the rotating airfoils, a higher pressure gradient may exist that may drive a high outflow of the wheel space air. Such a high outflow may starve or lessen the ability of the available cooling air to prevent ingestion downstream of the higher pressure regions.
There is a desire therefore for improved sealing mechanisms so as to minimize the loss of secondary cooling air through the wheel spaces. Reduction in the loss of the cooling air flow should improve overall gas turbine performance and efficiency.